In the manufacture of hollow plastic pieces by the blow method, powder or granular raw materials are usually first softened in an extruder (or in several extruders for multi-layered hollow pieces) by being heated under pressure, and then molded into a hollow tube, known as a preform blank, and formed with a blow or tube head whereby the tube is attached to an opening from the extruder. The tube is carried so as to be disposed generally vertically downwardly to between separated parts of a blow mold divided in the vertical plane. Next, the mold parts are closed and the preform blank is blown into a hollow piece of the desired shape in the blow mold chamber formed by the closed mold parts. Although articles having more than simply rotation symmetrical can be molded by this method, nevertheless only relatively minor deviations on either side of the plane of symmetry and its axis are permitted. One example of a product that can be so produced is a watering can with a handle. However, special measures must be taken to produce hollow pieces with several axes which are disposed at angles extending in three dimensions in relation to each other, e.g., pipe fittings with several curves or wave shaped curves. Such fittings may have three or more distinctive axes. The articles so produced are currently used extensively in industry, such as the automobile industry. For this purpose, European Patent 0 256 442 B1 teaches that the closing mount of a blow machine be tilted with the mold carrier and the halves of the vertically divided blow mold halves being suspended from the same, together with the motor used to unite and separate the halves, to move about a horizontal axis located outside the middle axis of the closing mount frame, while simultaneously sliding the frame carrying the closing mount on horizontal X- and Y-axes. In a variation of the machine described and illustrated in European Patent 0 256 442 B1, one of the mold halves can also be moved parallel to the other, i.e., moved up and down. By tilting the mold half intended to receive the tube shaped pre-molded part or preform blank in different angle positions, and by moving the closing mount back and forth and from side to side, and if necessary by shifting the height of one mold half opposite the other, the latter can be--with appropriate guidance--presented to the protruding heated tube on preform blank in such manner that a part of the mold chamber, running in a specific direction of the mold chamber, can take up certain parts of the blank without a deviation of the axis. This embodiment, however, has disadvantages in that its construction is relatively complicated, that many heavy parts must be moved, and that it allows little or no space under the closing mount. The introduction of the blowing agent into the pre-molded part located in the mold chamber, and if necessary the so called "calibration," i.e., the determination in relation to the inside diameter, of the collar opening of the blown hollow piece is, in most cases, provided by introducing it from above into the pre-molded part, which here is open. There are also situations, depending on the shape and size of the hollow piece to be produced, in which it appears to be more appropriate to introduce the air supply and/or carry out a calibration from below, i.e., a blow mandrel is introduced into the lower open end of the pre-molded part or blank, and in such cases it is considered a disadvantage if the moving unit supporting the blow mandrel must be moved together with the entire closing mount in order to tilt same.
A blower mechanism, according to German Patent 29 27 098 C2, uses another method. Here, the mold is provided with a horizontal separator, and its closing mount, in addition to opening and closing, moves only as a whole along the Z-axis, i.e., it can only be raised and lowered. Movements along the X and Y axes require sliding the extruder as such, together with the attached blow head. In a modified embodiment, movement along the Z-axis is not provided by raising and lowering closing mount, but rather by moving the blow head vertically opposite the extruder. Whereas in the first embodiment, the horizontally divided mold is hinged, thus making the lower horizontal half of the mold readily accessible to the extruder, after the upper half has been tilted down, in the second embodiment, the lower horizontal mold half is moved away from--on a straight or curved path--the area of the upper mold part located vertically above it to make it accessible to the moving extruder with the blow head. A fundamental disadvantage of this latter device is that it is more difficult to handle and to introduce into the mold chamber a plastic shaped pre-molded tube part, suitable for being blown into a hollow piece, which protrudes horizontally from the blow head nozzle, compared to a tube part which is extruded from the nozzle of the blow head vertically and downwardly, a difficulty which becomes more pronounced in the utilization of mold chambers for hollow pieces having multiple axes.
Another known blow molding apparatus in which the lower horizontal blow mold half is moved on a curved path, usually a circular path, then filled at one station and next closed at another, has the disadvantage that the time needed to bring the upper mold half onto the lower one for effectively closing the mold, is relatively long. Depending on the length of time, the pre-molded part remains in the lower mold half, cooling of the contact surfaces within the mold chamber occurs which can lead to problems during the subsequent blowing operation.